The invention relates to a recording element in which information can be recorded and read optically, and which comprises a supporting plate and a recording layer which layer is provided on the supporting plate and which comprises a squarylium dye.
Such a recording element is known from J. Vac. Sci. Technol., Vol. 18, No. 1 (January-February, 1981). The squarylium dye in question is a 4-dimethylamino-2-hydroxyphenyl-squarylium compound which corresponds to the formula ##STR1##
The disadvantage of the known element is that the squarylium dye used therein is soluble only in reactive and aggressive solvents, for example, primary and secondary amines. As a result of this the manufacture of the element is considerably impeded. Further solutions of the dye in the amines are not stable. The dye degrades considerably. According to the IBM Technical Disclosure Bulletin Vol. 22, No. 10, March 1980, the solubility of this dye can be improved by replacing a CH.sub.3 -group of the dimethylamino group by a long alkyl group. The squarylium dyes thus modified dissolve in hot ethanol, in hot acetone, in cold chloroform and in cold methylene chloride. However, the spin coating of hot solutions on the supporting plate so as to provide a dye layer presents problems. The solvents chloroform and methylene chloride attack the supporting plate if it is manufactured from, for example, an acrylate synthetic resin.
The above squarylium dyes have a low light absorption at a wavelength of 800 nm and higher so that the AlGaAs laser which is cheap and interesting in itself cannot be used for writing information. The low absorption also means that reading or display of information presents problems. Furthermore optical structures in the form of, for example, recording tracks or guide tracks cannot be provided in the recording layer of the known squarylium dye, which tracks are considered to be of great importance both for recording information and for reading recorded data.